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Some studies, for instance, indicate that short sleep duration increases levels of the gut hormone, ghrelin, which makes us feel hungry and often leads to increased eating.

Poor sleep might also increase the reward value of eating by making certain foods seem more attractive and increasing our motivation to obtain them. This idea is supported by recent research using functional magnetic resonance imaging (fMRI), which measures activity in specific regions of the brain by detecting changes in blood flow.

The study found that, in people with limited sleep, the brain regions associated with reward “lit up” more in response to pictures of tasty food, suggesting that sleepy people found these foods more appealing.

At the same time, lack of sleep might also impair our ability to make decisions and exert self-control over food intake.

In another recent brain imaging study, 23 healthy people had a night of normal sleep and a night of total sleep deprivation followed by fMRI scans.

After sleep deprivation, there was greater activity in the amygdala region of the brain (which is important for reward behaviour) in response to pictures of food. Sleep-deprived participants also reported a greater desire specifically for high-calorie foods compared to low-calorie foods.

At the same time, the scans showed other regions of the brain believed to be important for “higher-level” brain function and self-control were less active after sleep deprivation. This means sleepy people may be less able to control what and how much they eat.